(More on how early abuse affects the brain,

Johnston agrees, saying that aggression has been called the "default" setting for human behavior. People turn aggressive, he says, "when you don't have the problem-solving means of talking, negotiating, when you can't get what you want."

Almost 11,000 attacks or fights with a weapon occurred in American schools during the 1996-97 school year.
Source: National Center for Education Statistics.

Yet aggression with fists -- the traditional approach -- makes no headlines in an era of armed aggression. Johnston says it's "self-evident" that guns are a "power symbol," adding "There's not anything unusual with a boy being fascinated with guns and knives. It's clear that even the sweetest, nicest little boy loves to shoot 'em up." Such behavior does not start to become dangerous, he says, until "other people start to be hurt." The spate of recent murders does not reflect the old male fascination with guns so much as "a lot of new factors, the easy availability of guns, the mass-media factor."